1. Field of the Invention
This invention relates generally to the fields of semiconductor, photovoltaic flat panel, or LCD-TFT device fabrication.
2. Background of the Invention
Acetylene is a hydrocarbon useful in many industrial applications, including in the manufacture of semiconductor devices. Typically acetylene is dissolved in a solvent and stored in conventional cylinders which are filled with a porous media. This is done to prevent the explosive decomposition of acetylene. Because acetylene is thermodynamically unstable as compared to is constituent elements (carbon and hydrogen) decomposition, once initiated, can lead to an explosion. Dissolving acetylene in acetone and using porous storage media greatly reduces this hazard, primarily by providing thermal mass and reducing the free volume in the cylinder.
When acetylene stored this way is withdrawn from a cylinder, a small amount of solvent may be entrained in the withdrawn acetylene. The amount of entrained solvent is dependent upon factors such as the cylinder pressure, temperature and the rate at which the acetylene is withdrawn from the cylinder. The amount of entrained solvent may also change as the total amount of acetylene stored in the cylinder decreases. It is possible that the amount of solvent in the acetylene can range from about 0.1% to about 1% or even depending on the flow rate of withdraw, up to about 10%.
The presence of solvent in acetylene may be quite detrimental to some processes used in the chemical and semiconductor industries (including processes used for producing logic components, memory components, flat panel components and photovoltaic components) which require a high purity acetylene supply. Many of these processes occur at very high temperatures, and at these temperatures solvents will often result in the formation of oxygen, which can be highly undesirable from a process standpoint.
Methods exist for supplying acetylene without solvent to industrial applications. For instance, acetylene packaged without solvent is available, but it is only stored in gaseous state (at pressures below about 35 psig), making the amount of volume capable to be provided very low. Likewise, it is possible to produce acetylene on site in order to avoid storing the acetylene in a solvent. However, producing acetylene on site through hydrocarbon cracking is a capital intensive operation and only usually practical for very high consumption rates. Another method of on site production of acetylene is through the hydrolysis of calcium carbide, however, this method results in acetylene that may be contaminated with water vapor and with any contaminants present in the water used for the hydrolysis.
In the semiconductor industry, amorphous carbon film deposition in plasma enhanced chemical vapor deposition (“PECVD”) reactors is becoming a widely accepted process for increasing the resolution from lithography processes (“hard mask process”). As a result, unsaturated hydrocarbons such as propylene and acetylene are starting to be used more in the electronics industry. In order to meet the high purity and process control requirements of the semiconductor industry, a means of delivery large volumes of high purity, solvent free acetylene is required. Solvent and porous media free acetylene cylinders are not practical for supplying the electronics industry for hardmasks as the storage capacity of the cylinders is too small. The number of cylinder changes for a given tool in high volume production would be excessive.
Consequently, there exists a need for improved methods and apparatus for to store and supply acetylene.